1. Field of the Invention
The present invention relates to data communication device and method in a mobile communication system, and in particular, a device and method for communicating data with selection transmit diversity (STD).
2. Description of the Related Art
Transmit diversity technology offers the advantage of receiver diversity without increasing receiver complexity. STD also makes the advantage of receiver diversity possible without requiring a great modification to the structure of a terminal, and thus increases the capacity of a reverse link in digital cellular mobile communication. Implementation of STD in mobile communications requires the use of plural antennas for a base station as well as the following.
The STD function in a mobile communication system requires a terminal that measures the channel qualities of signals received from antennas of a base station, as well as receives data, and notifies the base station of the measurement result. For this purpose, the base station has forward link common channels assigned to the respective antennas, which are mutually orthogonal. The terminal compares the channel qualities of the antennas by the forward common channels assigned t the respective antenna, and transmits an antenna selection message to the base station to tell the base station to send data through the best channel quality antenna.
In operation, the terminal measures the channel qualities of the antennas for a predetermined time, and sends the base station the antenna selection message for selecting a transmission antenna on the basis of the measurement. Here, the predetermined time is an integer multiple of a power control group (PCG). The base station sends the terminal an antenna reference signal indicative of an antenna in current use for transmission. Then, the terminal can detect the transmission quality of the antenna selection message by comparing the base station antenna used for current transmission data with the antenna selected by the terminal.
FIG. 1 is a block diagram of a conventional STD transmitting device in which a common channel signal is transmitted through each transmission antenna and data is transmitted through a transmission antenna selected based on an antenna selection message received from a terminal. In this example, two transmission antennas are associated with a base station.
FIG. 2 illustrates the operation of the conventional STD transmitting device of FIG. 1, in which common channel signals are transmitted consistently through corresponding transmission antennas 151 and 153, and data is transmitted through a transmission antenna selected based on an antenna selection message received at a predetermined rate.
Referring to FIGS. 1 and 2, first and second common channel transmitters 11 and 12 are of the same configuration. They generate common channel signals to be transmitted via the first and second antennas 151 and 153, respectively. The first common channel transmitter 11 is comprised of a multiplexer 111 for multiplexing a pilot signal and data and a channel transmitter 113 for subjecting a common channel signal received from the multiplexer 111 to channel coding, rate matching, channel interleaving, orthogonal code modulation, and PN (Pseudo-Noise) sequence spreading. The second common channel transmitter 12 is comprised of a multiplexer 121 for multiplexing a pilot signal and data and a channel transmitter 123 for subjecting a common channel signal received from the multiplexer 121 to channel coding, rate matching, channel interleaving, orthogonal code modulation, and PN sequence spreading.
A traffic channel transmitter 13 generates traffic data to be transmitted from the STD transmitting device. In the traffic channel transmitter 13, a pilot selector 135 generates a corresponding pilot signal in response to an antenna selection message AS fed back from the terminal. A multiplexer 131 multiplexes the pilot signal received from the pilot selector 135 and traffic channel data. A channel transmitter 133 subjects the traffic channel signal received from the multiplexer 131 to orthogonal code modulation and PN sequence spreading.
A switch 141 switches the traffic channel signal based on the antenna selection message AS, and has an input terminal coupled to the output terminal of the traffic channel transmitter 13, a first output terminal directed toward the first antenna 151, and a second output terminal directed toward the second antenna 153. Hence, the switch 141 switches the traffic channel signal to the first or second antenna 151 or 153 according to the antenna selection message AS. An adder 143 adds a signal received from the first output terminal of the switch 141 and a signal received from the first common channel transmitter 11 to provide a signal indicated by 214 in FIG. 2. An adder 145 adds a signal received from the second output terminal of the switch 141 and a signal received from the second common channel transmitter 12 to provide a signal indicated by 216 in FIG. 2. A first RF (Radio Frequency) transmitter 147 is coupled between the adder 143 and the first antenna 151, and a second RF transmitter 149 between the adder 145 and the second antenna 153, for converting their corresponding transmit signals to RF signals.
In the conventional STD operation, common channel signals to be transmitted through the antennas 151 and 153 are generated by multiplexing pilot symbols and data and subjecting the multiplexed signals to spectrum spreading. A traffic channel signal is generated by multiplexing a pilot symbol and data selected based on message AS and subjecting the multiplexed signals to spectrum spreading. The resulting traffic channel signal and a corresponding common channel signal are added into the signal as indicated by 214 or 216 of FIG. 2 to be transmitted via an antenna selected by the antenna selection message AS indicated by 212 of FIG. 2. The unselected antenna sends a common channel signal 214 or 216 alone.
The above conventional technology, however, has the shortcoming that a base station always sends common channel signals through corresponding plural antennas. Since all the users in a cell do not own terminals adapted to STD, continuous transmission of the common channel signals for some STD terminals results in a waste of forward code resources and transmit power.
An object of the present invention, therefore, is to provide a STD communicating device and method in a mobile communication system.
Another object of the present invention is to provide a STD transmitting device and method in a mobile communication system, in which a common channel signal is transmitted through a transmission antenna and a traffic channel signal is transmitted through a transmission antenna selected based on an antenna selection message, to thereby enable efficient use of forward code resources and transmit power.
To achieve these and other objects, there is provided a STD communication device and method. In a STD communication method according to the present invention, a base station selects a transmission antenna corresponding to an antenna selection signal received from a terminal, transmits a traffic channel signal through the selected antenna, and transmits a predetermined part of the traffic channel signal through an unselected antenna.